It is generally known in the food industry to coat foodstuffs such as sausage material, for example, with a coating (hereinafter also referred to as coating composition and also called “sausage casing”). For such casings, use is made of compositions which can be directly applied in liquid form onto foodstuffs by, for example, co-extrusion or by immersing the foodstuff in the coating composition or spraying it therewith. Casings can also be manufactured by extrusion, for example, and then be filled with a foodstuff.
The coating is usually gelled, optionally after application to the foodstuff, by bringing it into contact with a gelling agent, as a result of which the coating material gels, therewith obtaining the desired hardness. In the case of co-extrusion, for example, this gelling takes place after the co-extrusion. When the casing is formed after extrusion, for example, it is then gelled before being filled with the foodstuff.
In particular in the case of extrusion or co-extrusion, the rheological properties and especially the viscosity of the coating composition play a major role. If the viscosity is too low, the composition deliquesces before it can be gelled, so that no cohesive casing can be formed. Too high a viscosity can lead to problems in extrusion and undesirable rippling of the casing. For this reason, apart from a gellable component, coating compositions generally contain a component to control viscosity.
From NL-C-102 930 a coating composition is known which mainly comprises water and the polysaccharide alginate, which composition would be suitable for co-extrusion around a foodstuff. Such alginate compositions, however, have been found to be unsatisfactory as coating compositions, because they do not meet the rheological properties which are desired for co-extrusion, for example: because of e.g. the low alginate content (4 w/w %) the viscosity of the composition according to NL-C-102 930, is too low (±30 Pa·s at 18° C.) to be applied with a satisfactory result in co-extrusion.
In order to obtain an acceptable viscosity, attempts were then made in the art to increase the alginate content, but it has been found that the desired viscosity can only be achieved with an alginate content of at least 8 w/w %. Such an alginate content, however, has the disadvantage that too strong gel formation occurs in gelling, leading to a foodstuff with a very unattractive appearance; the risk of rippling and cracking of the casing is thus very high. It has also been found that such an alginate casing from the technical point of view exhibits unsatisfactory adhesion to the food preparation, so that a food product is obtained around which there is a rather loose-fitting alginate casing.
Casings based on collagen are also generally known in the art, and these have been used for a few decades, reference being made for example to NL-A-690339, EPA0 619 077 and WO93/12660.
In the case of co-extrusion in particular, however, collagen has the disadvantage that after application of the casing to the foodstuff the collagen layer is highly vulnerable and should be hardened by removing water and by crosslinking the collagen. The removal of water generally takes place in a brine bath, while the crosslinking generally takes place in a chemical reaction by means of smoking or with the aid of liquid smoke, active crosslinking constituents thereof or smoke derivatives. In this connection reference is made to WO 93/12660. Other suitable crosslinking agents are generally known in the art, such as glutaraldehyde for example. The above-mentioned treatments, however, can have an unwanted effect on the taste of the coated product or product to be coated.
Another significant disadvantage of foodstuff casings containing collagen is that the collagen is of animal origin and is therefore unsuitable for coating vegetarian and kosher food products, for example.
An additional but significant disadvantage for application of protein of animal origin lies in the fact that animal products, and thus also animal protein, are usually barred when a disease such as e.g. BSE or swine fever is found in the animals in question, in order to avoid any risk to public health. In addition, bovine protein may be a carrier of diseases transmissible to man, such as Creutzfeldt-Jakob syndrome for example. In view of the above, the reliability of delivery of animal protein, and thus of coating material which contains it, may be adversely affected, among other things because under many national legislations the manufacturer must be able to prove that his products originate from healthy animals.
Because of the disadvantages of collagen, coating compositions have been produced which do not contain any collagen. Thus WO-99/55165 describes a collagen-free coating composition which comprises a combination of negatively charged gellable polysaccharides with a protein, where both the polysaccharides and the protein can work as gellable constituents, as well as for control of the viscosity. For this purpose such a composition contains 10 w/w % or more protein, which can also be of animal origin.
When protein in such quantities has been incorporated into a coating composition, this often leads to a coating with suboptimal properties. It is thus necessary to crosslink the coating composition after co-extrusion, which, as has already been described above, may affect the taste of the food product, and many proteins tend to colour the casing when the food product given a casing is boiled or fried, for example.
It is therefore an object of the invention to provide a coating composition which has the desired rheological properties, which can be formulated independently of proteins, with which a sufficiently robust and stable casing can be formed using the extrusion or co-extrusion techniques that are commonly used in the food industry.
Surprisingly, this object is achieved through an improved coating composition for foodstuffs of the above-mentioned type, in which the composition comprises at least a second polysaccharide which is neutral in the composition. The concept “neutral polysaccharide” is generally known in the art; this means a polysaccharide which essentially does not contain any charged groups and is preferably free of charged groups. The neutral polysaccharide is uncharged at pH values which are commonly used in the food industry when using polysaccharide-based coating compositions. Thus, the pH value will preferably lie between 4.0 and 9.5 when alginate for example is used in the composition; when pectin is used, the pH preferably lies between 2.0 and 9.5. When alginate in particular is used, these pH values lie more preferably between 4.5 and 7.5, even more preferably between 4.0 and 6.0, even more preferably between 4.5 and 5.5 and most preferably the pH is 5.0.
By incorporating a polysaccharide which is neutral at such a pH value it is possible to obtain a coating composition which possesses the rheological properties required for extrusion or co-extrusion. Neutral polysaccharides have been found to be eminently suitable for setting the right viscosity of the composition, essentially without adversely affecting the gelling of the gellable polysaccharide. The invention thus makes it possible to provide a polysaccharide-based coating composition with which casings are produced which possess sufficient robustness and are essentially not vulnerable to damage in subsequent treatments. Examples of suitable neutral polysaccharides are cellulose, methylcellulose, hydroxypropylcellulose, methylethylcellulose and galactomannans (such as e.g. guar gum, tara gum and carob meal).
The expression “not adversely affect the gelling” means that by addition of the relevant neutral polysaccharides in a solution of gel-forming polysaccharides, such as alginate for example, gelling of the gel-forming polysaccharides is possible in a comparable way and to a comparable extent as in the absence of the neutral polysaccharides, when gelling is carried out in the way that is usual in the art.
The term “polysaccharide” also includes salts and acids of polysaccharides, as well as combinations thereof, and of combinations of two or more polysaccharides. The polysaccharides of the coating composition according to the invention are preferably edible polysaccharides, in order to provide an edible coating.
Foodstuffs which can be coated with the composition according to the invention are generally known in the art, and include for example paste-like food preparations for the production of various types of sausage and other meat and fish products or products which contain vegetables and/or cheese, for example.
Another advantage of the invention is that the casing does not need to contain any proteins, so that the above-mentioned disadvantages of casings containing proteins are avoided, such as for example the colouring of the coated foodstuff when this product is boiled and/or fried.
With the composition according to the invention it is thus possible to obtain a satisfactory casing for a foodstuff, in which the disadvantages of protein, especially collagen, such as those associated with water removal and crosslinking, can be obviated—which can yield considerable savings in equipment and production time. Because the casing does not need to be crosslinked after gelling, it is also possible, with the composition according to the invention, to give fresh products a coating skin—something which has hitherto been found to be scarcely possible with coating compositions based on collagen, because of the crosslinking reaction with liquid smoke which affects the taste.
Negatively charged polysaccharides which gel under the influence of cations (hereinafter referred to as gel-forming polysaccharide) are generally known in the art and have been used for several decades in the food industry. Such a polysaccharide, or a salt or acid thereof, is usually dissolved in the coating composition and the polysaccharides are gelled by bringing them into contact with a solution which contains cations. The cations undergo an electrostatic interaction with the gel-forming polysaccharides, as a result of which the latter form an undissolved complex with the cations and thus gelling occurs. Depending on the polysaccharide used, monovalent or bivalent cations are applied for this purpose, as is known to the person skilled in the art. It is thus known, for example, that carrageenan gels in the presence of K+ ions and that alginate gels in the presence of bivalent ions, preferably Ca2+ ions.
In the coating composition according to the invention the first polysaccharide is preferably chosen from the group consisting of alginate, pectin, carrageenan or a combination of two or more thereof. Said polysaccharides, especially alginate, have been found to be highly suitable for use as the gel-forming polysaccharide in the coating composition according to the invention.
When pectin is used as the gel-forming polysaccharide, the preferred form is low-esterified pectin, in which less than 50% of the carboxylate groups of pectin is esterified with a methyl group (methyl alkylate). The low-esterified pectin has been found to be highly suitable for forming a good-quality coating skin.